Hemodialysis and related processes are used to treat large numbers of patients suffering from renal failure and other conditions, including both acute and chronic conditions. However, improvement is still needed in, among other features, the length of time that an individual filter cartridge can be used without suffering from clot formation and filter clogging. There also is a need, for whatever fluid is flowing in the inter fiber space, for more uniform flow distribution in the inter fiber space, with stagnation regions being either non-existent or as small as possible.